SPPersistedUpgradableObject is a SPPersistedObject that implements the IUpgradable interface. The MSDN is seriously lacks any documentation other than it:
Provides members for managing an upgradable object
It seems to be related to caching and reloading the object from the database but i can't find confirmation of this anywhere.
So really my question do:
SPWebapplication wa = SPContext.Current.Web.Site.WebApplication;
wa.Invalidate() //causes object to be reloaded from database on next access?
and
wa.Upgrade(); //causes object to be reloaded from the database?
actually do what i think they are doing?